Advice from the UGA Extension: All about tomato fertilizer

While reading several commercial fertilizers for my tomato plants a couple of weeks ago, I realized marketing, like in most things, plays a huge role in the selling of fertilizers for specific crops. Tomatoes are one of those crops. Make sure that when you are deciding on a fertilizer for your tomatoes, you don’t let the marketing ploys get you. Here are a few things to look out for when fertilizing tomatoes.

First, the most important thing to do when planting tomatoes is taking a soil sample. These samples will provide explicit details on what to fertilize your tomatoes and whether you should alter your soil’s pH.

In the absence of a soil sample, you should apply lime at a rate of 5 pounds per 1,000 square feet to ensure your pH is adequate enough for production. You should also apply 1.5 pounds of 10-10-10 fertilizer for 100 square feet of row. These numbers mean there are 10 units of nitrogen, 10 units of phosphorus, and 10 units of potassium in the fertilizer. You will find that the vast majority of your fertilizers are comprised of some blend of those three nutrients. However, most plants require up to 17 nutrients, 14 which come from the soil. Check your fertilizers to ensure it has some other nutrients like magnesium, calcium, sulfur, zinc, and boron. Super Rainbow is an excellent example of a premium fertilizer that contains lots of the elements needed for tomato fertilization.

One of the most important nutrients for tomato production is calcium. If you’ve ever grown tomatoes before, you’ve likely experienced blossom end rot. BER is caused by a deficiency or problem with calcium uptake. To prevent this, you should ensure you apply enough calcium to reduce your incidence of blossom end rot.

After knowing what to use for fertilizer, you should know when to fertilize. The 5 pounds of lime and the 1.5 pounds of Super Rainbow or another premium fertilizer should be applied to the soil and mixed in prior to planting. At the time of planting, you should give them a very light amount of fertilizer (2 tablespoons of 5-10-10 dissolved in water). After planting, applying one pound of gypsum per 100 square feet will assist in reducing the BER incidence. As the first tomatoes form on the vine, another pound of 10-10-10 can be applied and repeated every 3-4 weeks until harvest is complete.

While we see lots of problems with under fertilizing tomatoes like a lack of calcium or a low pH, we also see similar issues from over fertilizing. If you apply fertilizers in amounts not needed or apply the wrong blends of fertilizer we can also see issues with calcium uptake, again causing BER, or we can see other concerns that reduce the production of your tomatoes. The best way to ensure your fertility program is correct is to take a soil sample.

Make sure you grow beautiful tomatoes this year by knowing what to look for in your fertilizers and how to fertilize. For questions, contact us at your local extension office at 478-237-1226.

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